/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.extensions.euphoria.core.translate;



import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.functional.UnaryFunction;

import com.bff.gaia.unified.sdk.transforms.DoFn;

import com.bff.gaia.unified.sdk.transforms.PTransform;

import com.bff.gaia.unified.sdk.transforms.ParDo;

import com.bff.gaia.unified.sdk.values.KV;

import com.bff.gaia.unified.sdk.values.PCollection;

import com.bff.gaia.unified.sdk.values.TypeDescriptor;

import com.bff.gaia.unified.sdk.values.TypeDescriptors;



import java.util.Objects;



import static java.util.Objects.requireNonNull;



/** Key extracting utility transformation shared among operator translators. */

class ExtractKey<KeyT, ValueT>

    extends PTransform<PCollection<ValueT>, PCollection<KV<KeyT, ValueT>>> {



  private static class ExtractKeyFn<KeyT, InputT> extends DoFn<InputT, KV<KeyT, InputT>> {



    private final UnaryFunction<InputT, KeyT> keyExtractor;



    ExtractKeyFn(UnaryFunction<InputT, KeyT> keyExtractor) {

      this.keyExtractor = keyExtractor;

    }



    @SuppressWarnings("unused")

    @ProcessElement

    public void processElement(ProcessContext c) {

      final InputT element = c.element();

      final KeyT key = keyExtractor.apply(element);

      c.output(KV.of(key, element));

    }

  }



  private final UnaryFunction<ValueT, KeyT> keyExtractor;

  private final TypeDescriptor<KeyT> keyType;



  ExtractKey(UnaryFunction<ValueT, KeyT> keyExtractor, TypeDescriptor<KeyT> keyType) {

    this.keyExtractor = requireNonNull(keyExtractor);

    this.keyType = requireNonNull(keyType);

  }



  @Override

  public PCollection<KV<KeyT, ValueT>> expand(PCollection<ValueT> input) {

    Objects.requireNonNull(input.getTypeDescriptor());

    return input

        .apply(ParDo.of(new ExtractKeyFn<>(keyExtractor)))

        .setTypeDescriptor(TypeDescriptors.kvs(keyType, input.getTypeDescriptor()));

  }

}